The present invention generally relates to mold handling systems, and more particularly relates to sand mold handling systems.
Molded metal castings are commonly manufactured at foundries through a matchplate molding technique which employs green sand molds comprised of prepared sand and additives which are compressed around cope and drag patterns mounted on opposite sides of a matchplate. The sand mold is thus formed in upper and lower matching portions, an upper cope mold, and a lower drag mold. The cope mold is formed in a separate cope flask which is filled with prepared sand and compacted onto the matchplate. The matchplate is then removed leaving an indentation in the cope mold of the desired shape for the upper portion of the casting. Simultaneously, the drag mold is formed in a separate drag flask. Usually the matchplate is in the form of a planar member with the pattern for the cope mold on one side and the pattern for the drag mold on the other. After the cope and drag molds have been formed, they are placed together to form a unitary mold having an interior cavity of the desired shape. The cavity can then be filled with molten metal through an inlet or xe2x80x9cspruexe2x80x9d provided in the cope mold to create the desired casting. Such a system is disclosed in Hunter U.S. Pat. No. 5,022,212.
As with many volume sensitive production operations, manufacturers are required to automate the manufacturing process in order to remain competitive. Foundries engaging in the casting of metal objects through the use of green sand molds are not immune to this reality. It is common in today""s marketplace, for the machine which produces the sand molds to be connected to a machine which fills the sand mold with molten metal, which in turn is connected to a machine for cooling the molten metal into a solid casting, which in turn is connected to a machine for removing the sand mold and revealing the casting for harvest. Such a system is disclosed in Hunter U.S. Pat. No. 4,589,467.
In the aforementioned ""467 patent, the sand molds are manufactured and communicated along a linear conveyor to a circular, rotating, or xe2x80x9ccarouselxe2x80x9d conveyor. Molten metal is introduced into the molds at one location on the carousel and the molten metal is then allowed to cool within the sand mold as the carousel rotates. The carousel is provided with both an outer diameter track and an inner diameter track which provide for additional cooling of the metal, and which increase the throughput of the machine.
While such a carousel system has enjoyed, and continues to enjoy, considerable commercial success, it is not without its drawbacks. In particular, if a manufacturer wishes to increase the throughput of a carousel-type molding machine, a carousel of a different diameter will necessarily have to be employed, at considerable additional expense. In addition, every time a new carousel is needed, a substantial down-time period is encountered wherein the machine is not producing castings, and which requires considerable labor to put into effect.
Similarly, if the cooling times of the metal being processed through machine are variable, the length of the cooling cycle will accordingly be affected. With a carousel-type conveyor, the cooling cycle time can be increased either by slowing the carousel, or by adding a carousel of a greater diameter. Conversely, if the cooling time is to be lessened, the rotational speed of the carousel can be increased, or a carousel having a smaller diameter can be added. However, both options are less than desirable. If the carousel is slowed, the throughput of the machine is proportionally diminished, and if a new carousel is added, additional expense is incurred due to increased downtime and additional equipment overhead.
U.S. Pat. No. 5,901,774 therefore discloses a linear mold handling system wherein separate double-deck pouring and cooling conveyors are provided. Sand molds are transferred to the pouring conveyor and indexed to a station in which molten metal is deposited into the sand molds. The molten metal filled sand molds are then transferred to a lower level of the pouring conveyor and then back to the upper level of the pouring conveyor before being transferred to a separate cooling conveyor provided laterally adjacent to the pouring conveyor. The embodiment disclosed in the aforementioned parent application provides a cooling conveyor which is three rows wide and includes a plurality of trays adapted to receive up to three molds disposed on the conveyor. The partially cooled sand molds are transferred from the pouring conveyor to the cooling conveyor and into one of the trays disposed thereon. Each tray is adapted to receive up to three sand molds. Once a tray is filled, it is indexed forward until reaching an end of the upper level of the cooling conveyor at which time the elevator lowers the trays to a lower level and then back to an upper level of the cooling conveyor before being pushed into a dump chute and a shake-out vibrating conveyor.
One issue that has arisen and has been discovered by the inventive entity of the present invention is that pouring metal into molds carried on the upper deck of a two tiered conveyor may limit the size of the mold to be used with the two tiered mold handling system. Because a worker manually pours metal into molds from a ladle, system design is thus faced with a limited worker height. Taller molds make it difficult to manually pour molten metal into the molds at higher elevations on the conveyor that is necessitated by the increased height of the molds.
It is an aim of the preferred embodiment of the present invention to provide a linear sand mold handling system with an ability to be tailored to the specific dwell time requirements of the metal being poured.
It is another aim of the present invention to provide a simplified sand mold handling system with reduced equipment requirements and thus reduced cost for both initial start-up and for maintenance over time.
It is an objective of the present invention to provide a linear sand mold handling system with improved volumetric capacity or throughput capability.
It is another objective of the present invention to provide a linear sand mold handling system with more uniform cooling in order to provide more physically reliable and predictable castings.
It is another objective of the present invention to provide for use of two-tiered mold handling systems with larger/taller molds.
Based on the foregoing, the present invention is directed broadly toward a two tiered mold handling system for use in a sand mold casting machine which comprises a two tiered conveyor for pouring and cooling, or two tiered conveyor for cooling only. The two-tiered conveyor has an upper linear track and a lower linear track disposed at a lower vertical elevation. The tracks carry a plurality of mold pallets along an endless path around the upper and lower linear tracks. It is believed that the present invention as claimed ties together several concepts including two tiered pouring conveyors in combination with two tiered cooling conveyors, two tiered combination pouring and cooling conveyors, and one tiered pouring conveyors in combination with two tiered cooling conveyors to provide a lower pouring elevation.
According to one aspect of the present invention, each mold pallet has a plurality of adjacent mold receiving locations such that each mold pallet is adapted to receive at least two sand molds side by side. This provides for parallel movement of molds. Indexing rams may be provided to shift the molds between the different mold receiving locations on each mold pallet.
According to another aspect of the present invention, the two tiered conveyor receives and discharges molds on the top track. It is a feature that a one tiered pouring conveyor may be provided adjacent to the two tiered cooling conveyor but at a lower elevation than the top track of the two tiered cooling conveyor to provide for a lower pouring elevation. An elevator is provided for elevating molds from the one tiered pouring conveyor to the upper track of the two tiered cooling conveyor. It is an advantage that this arrangement allows for indexing or shifting of molds laterally can be done on the top track.
Other objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.